The majority of cluster mills for cold rolling metal strip have been provided with monobloc housings of the type shown in U.S. Pat. Nos. 2,169,711; 2,187,250; and 2,776,586, or of the improved type taught in U.S. Pat. No. 3,815,401, and also illustrated in FIGS. 1a and 1b herein.
The advantage of the monobloc housing over any other housing type is great rigidity which is required in order to roll strip having the greatest uniformity in thickness. It will be noted by one skilled in the art that, as time progresses, requirements for gauge accuracy (i.e. thickness uniformity) are becoming increasingly stringent.
However, there are some disadvantages with respect to the monobloc housing, which, for some applications, can cause serious difficulties. These disadvantages can be summarized as follows:
Firstly, if a mill wreck occurs, i.e. the strip breaks and then accumulates in a tangled mass of scrap inside the housing, it sometimes takes several hours to remove the tangled strip, to enable rolling to recommence, and so significant lost production occurs. It would be advantageous in such cases to be able to separate upper and lower halves of the housing to provide more room for removal of scrap strip. This is particularly important for high speed mills.
Secondly, for some applications, it would be advantageous to be able to roll with a larger range of work roll diameters than can be achieved with a monobloc housing.
Thirdly, the ability to separate upper and lower halves of the housing would facilitate threading of the strip.
Fourthly, the ability to mount force measuring devices between upper and lower halves of the housing would enable more accurate measurement of roll separating force, which could be useful for purposes of data logging and improving accuracy of automatic gauge control systems.
Prior art alternative housing designs have overcome some of these difficulties in some cases and, in other cases, have overcome all of the difficulties, but paid the penalty of a great reduction in mill rigidity. Some examples of such prior art are shown in FIGS. 2, 3a and 3b.
In FIG. 2, the housing is made in two halves, an upper half 112 and a lower half 113 which are clamped together using four hydraulic cylinders 115 (one at each corner) and fixed spacers 116 to separate upper and lower halves at a predetermined spacing. This design gives a rigidity close to that of the monobloc housing, but permits the upper and lower housing halves to be separated by operating the hydraulic cylinders in the appropriate direction. With this design, all four difficulties can be overcome, but two disadvantages remain. One is that it is necessary to change spacers 116 to permit a substantial change in work roll diameter. This is an inconvenience in applications where such diameter changes are frequent. Secondly, if there is a substantial change in work roll diameter, and spacers 116 are changed to suit, then the pass line height changes, because the lower housing is fixed. This can cause difficulties because other devices such as work roll thrust bearings, strip wipers, thickness gauges, mill drive spindles all operate best at a fixed pass line level.
In FIGS. 3a and 3b the mill housing is split into two halves and reduced in width so that the two halves can fit in the windows of two four-high type mill housings, utilizing the standard screwdown and pass line height adjusting mechanisms built-in to the four-high housings. FIGS. 3a and 3b show a hydraulic screwdown cylinder 109 at the bottom of each housing window and a screw 108 and nut for pass line height adjustment at the top of each housing window. This design overcomes all four of the above difficulties, but gives a much less rigid (and much more expensive) structure than the monobloc housing.
The present invention is based upon the discovery that a mill housing assembly for a cluster mill can be provided having substantially the same size, form and structure as a conventional monobloc mill housing. The mill housing assembly of the present invention is divided along a horizontal plane close to or at its horizontal center line into an upper mill housing and a lower mill housing. By provision of jack and screw assemblies at the four corners of the mill housing assembly, and by provision of adjustable tie rod means at the four corners of the mill housing assembly, a structure can be provided which compares favorably with a monobloc mill housing from the standpoint of rigidity, while possessing all of the advantages of a two-piece mill housing including the ability to separate the upper and lower mill housings to clear wrecks, a wide range of roll gap settings, and the operation of a fixed pass line level.